1. Field of the Invention
The present invention relates to a thin-film transistor (TFT) and a zinc oxide-based sputtering target for the same, and more particularly, to a barrier film of a TFT and an indium oxide-doped zinc oxide-based sputtering target that is used for deposition of the barrier film.
2. Description of Related Art
A liquid crystal display (LCD) or an electroluminescent display (EL) has superior displaying performance and consumes little power. Therefore, the LCD or EL is widely used for display devices of mobile phones, personal computers (PCs), word processors, TVs or the like. These displays operate using transistors, namely, thin-film transistors (TFTs) which are formed of fine patterns. As for formation of TFTs, a thin film layer which has semiconductor characteristics is required to be formed between electrodes.
Such a semiconductor layer is made of amorphous silicon (Si) or polycrystalline Si, both of which have advantages and disadvantages. For instance, amorphous Si is advantageous in that it can be easily deposited on a large area and its manufacturing cost is inexpensive. However, amorphous Si has low mobility, i.e. the ability of amorphous Si to allow electrons to migrate through the semiconductor layer is low. Therefore, it is difficult to apply amorphous Si to high-definition displays, which is problematic. In contrast, the mobility of polycrystalline Si is at least 100 times the mobility of amorphous Si, which is advantageous for realizing the image quality of an organic light-emitting diode (OLED) or LCD in the level of ultrahigh definition. However, it is difficult to deposit polycrystalline Si on a large area, which is a disadvantage against its application to a large TV. In addition, the manufacturing cost of polycrystalline Si is high, which lowers the price competitiveness of a product.
In order to overcome these problems, many attempts have been made by a number of research groups in order to substitute the semiconductor layer with an amorphous oxide. Oxide semiconductor can be easily deposited on a large area by sputtering that is a common method of forming a film of a transparent electrode. In addition, oxide semiconductor has high mobility that is 10 to 50 times the mobility of amorphous silicon. Therefore, attempts to apply an oxide semiconductor to mobile devices that require low power consumption are actively underway. In addition, research intended to spread the application of this technology to TVs is also underway.
As a sputtering target used for depositing an oxide semiconductor layer, a sputtering target that is generally composed of four elements of In, Ga, Zn and O is well known.
Here, it is known that the ratio of these elements In:Ga:Zn is 1:1:1 or 2:2:1. In a TFT device, when the oxide semiconductor layer is deposited by sputtering, source and drain electrodes are generally deposited on top of the oxide semiconductor layer. Since these electrodes do not have adequate electric contact with an oxide that has a higher resistance and the danger of diffusing into the oxide semiconductor layer, a barrier film made of Ti or a material such as Cu—Mn is interposed between the oxide semiconductor layer and the electrodes.
Recently, the application of a copper electrode that can exhibit a high level of performance is being examined as an electrode material, and the problem in that Cu and Ti diffuses into the oxide semiconductor layer is becoming an issue. Therefore, a barrier material that improves the contact between a Cu electrode and the oxide semiconductor layer, prevents Cu from diffusing into the oxide semiconductor layer, has superior etching selectivity in relation to the oxide semiconductor layer, and does not create problems such as an undercut, due to etching, is gaining more interest.
The information disclosed in the Background of the Invention section is provided only for better understanding of the background of the invention, and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.